Linear ethyleneamines are known for their many uses in industry. For example, ethylenediamine (EDA) (1,2-diaminoethane) is a strongly basic amine in the form of a colorless liquid having an ammonia-like odor. EDA is a widely used building block in chemical synthesis, with approximately 500,000,000 kg being produced in 1998. EDA is used in large quantities for production of many industrial chemicals, such as bleach activators, fungicides, chelating agents, plastic lubricants, textile resins, polyamide resins, and fuel additives. Diethylenetriamine (DETA) can be used primarily as an intermediate to manufacture wet-strength paper resins, chelating agents, ion exchange resins, ore processing aids, textile softeners, fuel additives, and corrosion inhibitors. Triethylenetetramine (TETA) has such major applications as epoxy curing agents, as well as the production of polyamides and oil and fuel additives.
It is recognized that linear polyalkylene polyamines (such as EDA, DETA and TETA) do not have the same industrial uses and demands as cyclic polyalkyleneamines such as piperazine (PIP). As such, it can be desirable to develop a process with sufficient selectivity in forming a linear polyalkylene polyamine to produce an amine composition with a relatively high ratio of a desired linear polyamine (e.g., DETA) to PIP.
One approach in producing linear ethyleneamines is reductive amination. Reductive amination (also known as reductive alkylation) involves reacting an amine or ammonia with a carbon-containing material. Reductive amination involves the conversion of a carbonyl group (typically a ketone or an aldehyde) to an amine. A classic named reaction is the Mignonac Reaction (1921) involving reaction of a ketone with ammonia over a nickel catalyst, for example, in a synthesis of alpha-phenylethylamine starting from acetophenone.
Reductive amination produces a variety of products, some of which have greater economic value than others, depending upon current market requirements. For example, the reductive amination of monoethanolamine (MEA) produces lower molecular weight linear ethyleneamines, such as EDA, aminoethylethanolamine (AEEA), and DETA. A minor amount of higher linear ethyleneamines, for example TETA and tetraethylenepentamine (TEPA) are also formed. In addition, cyclic ethyleneamines, such as PIP, hydroxyethylpiperazine (HEP), and aminoethylpiperazine (AEP) are also formed. Cyclic ethyleneamines tend to be less valuable than acyclic ethyleneamines. Accordingly, for maximum economic benefits the catalyst compositions used in commercial reductive amination processes should be selective to the desired mixture of amine products, in addition to being highly active.
It is appreciated in reductive amination art that reductive amination catalysts must first be reduced before effecting the reaction, and then hydrogen gas employed during the course of the reaction in order to maintain catalytic activity and selectivity. During the reaction, reductive amination typically requires addition of ammonia.
One drawback relating to the catalysts and processes that have been described for reductive amination to produce linear polyamines is that they do not typically provide high selectivity to DETA. In these processes, as MEA conversions are increased to produce more DETA, PIP production becomes a significant problem. PIP can be formed from ring closure of DETA or AEEA. Catalysts which are promoted with precious metals are known to show improved activity and selectivity for the reductive amination of MEA to EDA; however, high levels of DETA in the product mix result in concurrent high levels of PIP. As a result, there is still a need for improved catalysts which give high EDA and DETA selectivities while minimizing the amount of PIP formed in the product mixture.
The reductive amination of lower aliphatic alkane derivatives, i.e., diols such as ethylene glycol and alkanolamines such as MEA, is a commercially important family of processes. A variety of catalyst compositions for this purpose is found in the literature and is used commercially. Many of these catalyst compositions are based on nickel/rhenium mixtures (such as nickel/rhenium/boron catalyst compositions and the like) deposited on a support material.
As an alternative to reductive amination, linear polyamines can be prepared by transamination. Transamination is a transfer of an amino group from one chemical compound to another, or the transposition of an amino group within a chemical compound.
Many of the catalysts disclosed for transamination are high metal loaded catalysts. Specifically, Raney nickel catalysts have been employed. These catalysts typically have small particle sizes, which makes their use in fixed bed processes difficult. To address difficulties with small particle sizes, more recent approaches have involved associating the catalytic metals with a support. However, such supported catalysts have typically included very large catalytic metal loading, and such high catalytic metal loading can create its own drawbacks. For example, U.S. Pat. No. 7,053,247 (Lif et al.) describes particulate catalysts containing 26 to 65% by weight of nickel on an oxide carrier. Catalyst compositions including such high levels of catalytic metals can be pyrophoric, more expensive, and do not appear to offer high selectivities for desirable transamination products (e.g., DETA).
Transamination reactions are typically performed at lower temperatures than reductive amination. A general problem in transamination processes of EDA to DETA and higher polyethylenepolyamines is the fact that at moderate temperatures and pressures, these processes can result in too high a proportion of cyclic ethyleneamine compounds, such as PIP, which requires that the EDA conversion be kept low.